Routing in Vehicular Delay Tolerant Networks: A Comparision

Introduction

Now days the internet acts as the backbone network for most systems that require communication. The goal of a communication network is to deliver a message from the source to the destination successfully. The success of end to end delivery is dependent on finding the best possible path or route between the ends, and therefore a good routing strategy is the key to efficient communication. Routing in the internet uses a connected graph where there is always a path or route from a node to every other node. It can have single path or multiple paths to a destination. To communicate using the internet it is necessary and sufficient to have at least one device element of the network to have access to internet. If, at any point in time either the sender, receiver or the device connected to internet have no connection, then the message will get dropped. As an example, TCP (Fall, 2003) is a widely used connection oriented protocol, in this before starting the conversation, the sender and receiver must establish an end to end connection. TCP sends the data using IP addresses and port numbers of the sender and destination. To send the data TCP uses three way hand shake procedure. The network have continues connectivity, very low packet dropping rate, stable network topology and low packet delivery delay.

But as vehicles that are constantly in motion, they have no stable end to end path, but only have intermittent connectivity among nodes. Thus Vehicular networks have unstable topology and frequent disruption of the connections. Traditional internet works poorly in such a challenged environment. Vehicular Delay Tolerant Network(VDTN) which are adaptation of DTN can provide communication in this type of challenged network. Vehicular networks can have large and unpredictable delay in delivery of messages. VDTN have very low delivery probability and have limited resources. Communication range between the nodes is not long enough to connect all the nodes. Contacts between the nodes are for uncertain and varied durations. So VDTN uses the contact between nodes as the opportunity to deliver the messages. DTN network has many routing approaches. Most of them are replication based.

The network in challenging environment may or may not have continuous connections between the nodes of the network. But data is required to get transferred to the destination even when there is, not a single path leading to destination from source. In order to transfer the data, data needs to keep flowing until it reaches the destination. And to keep data flowing nodes need to interact with each other to transfer the data they have to each other (Keränen, 2009). VDTN can help in a great and efficient way to keep that data flowing in vehicular mobile challenged networks. DTN can provide an opportunistic network with mobile nodes such as a network built of moving sensors on pedestrians, animals and vehicles (Juang, 2002).

DTN overcomes all the problems like sporadic connectivity, prolonged and unpredictable delays, uneven data rates and high data rates by using Store-Carry-Forward Message Switching (Keränen, 2009). The whole packet (all complete blocks of application data) or the fragments of these messages are transferred or forwarded from a buffer storage of a node to the buffer storage of another node, on a path that will lastly reach to the destination. Due to frequent disruptions of the network, nodes need to communicate during the opportunistic contacts. Opportunistic contacts are the unscheduled contacts (Burleigh, 2007). DTN uses this property (mobility) of nodes as an opportunity for delivering messages between source end and the destination end by passing it on to any other nodes that comes within the range of communication of that node (Mealling, 2002). The mobile nodes then carry messages to help network to deliver them to destination. With growth in internet communication technology and advent of even 5G communication, vehicular networks will be able to use mobility to their advantage (Agrawal, 2016), (Agrawal, 2017), (Agrawal, 2018), (Agrawal, 2019).